Programmer : Dhiren Patel

   Platform  : NT 4.0 Workstation
 
   Compiler  : VC++ 5.0
 
   Date   : April 21, 1998

   Copyright  : You are free to distribute this source code provided this header is not removed and
   not altered in any way without prior written permission from the programmer.

*************************************************************************/
 

#include <stdio.h>
#include <conio.h>
 

/*************************************************************************

 Function DMY

 Parameters  : Character Pointer to two date strings in DayMonthYear format.

 Return Value : Returns an integer specifying the no of days between
       two dates. If illegal dates are entered, then a 0 is returned
 
 Programmer  : Dhiren Patel

 Comment   : Standard library calls are avoided so that the function can be compiled and used in
   any  other languages without requiring the libraries and also to keep the function small.

   Copyright  : You are free to distribute this source code provided this header is not removed and
    not altered in any way without prior written permission from the programmer.

****************************************************************************/

int DMY(char* ststr,char* edstr)
{
 int i,flag = 0;
 int days = 0;
 int styr,stmth,stdt;
 int edyr,edmth,eddt;
 
 for(i=0; ststr[i] != '\0'; i++);
 
 if(i != 8)
  return 0;
 
 for(i=0; edstr[i] != '\0'; i++);
 
 if(i != 8)
  return 0;

 /*extracting dates from string */
 styr  = (ststr[4]-'0')*1000 + (ststr[5]-'0')*100 + (ststr[6]-'0')*10 + (ststr[7]-'0');
 stmth = (ststr[2]-'0')*10 + (ststr[3]-'0');
 stdt  = (ststr[0]-'0')*10 + (ststr[1]-'0');

 edyr  = (edstr[4]-'0')*1000 + (edstr[5]-'0')*100 + (edstr[6]-'0')*10 + (edstr[7]-'0');
 edmth = (edstr[2]-'0')*10 + (edstr[3]-'0');
 eddt  = (edstr[0]-'0')*10 + (edstr[1]-'0');

 /*if same dates */
 if (styr == edyr)
 {
  if( stmth == edmth)
  {
   if( stdt == eddt)
   {
    return 0;
   }
   else if(stdt > eddt)
   {
    i = stdt; stdt = eddt; eddt = i; flag = 1;
   }
  }
  else if( stmth > edmth)
  {
   i = stmth; stmth = edmth; edmth = i; flag = 1;

   i = stdt; stdt = eddt; eddt = i;
  }
 }
 
 
 /*reverse the dates */
 if (styr > edyr)
 {
  i = styr; styr = edyr; edyr = i; flag = 1;

  i = stmth; stmth = edmth; edmth = i;

  i = stdt; stdt = eddt; eddt = i;
 }

 /*checking for wromg date and year */
 if( stmth > 12 || stmth < 1 || edmth > 12 || edmth <1 || stdt > 31 || stdt < 1 || eddt > 31 || eddt < 1)
  return 0;

 /*checking for wrong date in feb styr */
 if( stmth == 2 )
  if (stdt > 28)
   if((styr % 4)!=0)
    return 0;
   else if(stdt != 29)
    return 0;
 
 /*checking for wrong date in feb edyr */
 if( edmth == 2 )
  if (eddt > 28)
   if((edyr % 4)!=0)
    return 0;
   else if(eddt != 29)
    return 0;
 
 /*if same edyr & styr */
 if(styr == edyr)
 {
  if(stmth == edmth)
  {
   days = days + (eddt - stdt);
   if(flag) return -days; else return days;
  }
  else
  {
   switch(stmth)   /* adding for stmth */
   {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
     days = days + (31-stdt); break;
    case 4:
    case 6:
    case 9:
    case 11:
     days =days + (30-stdt); break;
    case 2:
     if((styr % 4) == 0)
     {
      days = days + (29- stdt);
      break;
     }
     else
     {
      days = days + (28-stdt);
      break;
     }
   }

   days = days + eddt;  /* adding for edmth */

   /* adding for months in between */
   if((edmth - stmth) > 1)
   {
    for(i = stmth + 1; i < edmth; i++)
    {
     switch(i)
     {
      case 1:
      case 3:
      case 5:
      case 7:
      case 8:
      case 10:
      case 12:
       days = days + 31; break;
      case 4:
      case 6:
      case 9:
      case 11:
       days =days + 30; break;
      case 2:
       if((styr % 4) == 0)
       {
        days = days + 29;
        break;
       }
       else
       {
        days = days + 28;
        break;
       }
     }
    }
   }
  }

  if(flag) return -days; else return days;
 }
 

 /*adding for in between years */
 if((edyr - styr) > 1)
  for( i = styr+1; i <= edyr-1; i++)
   if ((i % 4) == 0)
    days = days + 366;
   else
    days = days + 365;
 
 /*adding for months of start year  */
 for( i = stmth+1; i < 13; i++)
 {
  switch(i)
  {
   case 1:
   case 3:
   case 5:
   case 7:
   case 8:
   case 10:
   case 12:
    days = days + 31; break;
   case 4:
   case 6:
   case 9:
   case 11:
    days =days + 30; break;
   case 2:
    if((styr % 4) == 0)
    {
     days = days + 29;
     break;
    }
    else
    {
     days = days + 28;
     break;
    }
  }
 }
 

 /*adding for months of end year */
 for( i = 1; i < edmth; i++)
 {
  switch(i)
  {
   case 1:
   case 3:
   case 5:
   case 7:
   case 8:
   case 10:
   case 12:
    days = days + 31; break;
   case 4:
   case 6:
   case 9:
   case 11:
    days = days + 30; break;
   case 2:
    if((edyr % 4) == 0)
    {
     days = days + 29;
     break;
    }
    else
    {
     days = days + 28;
     break;
    }
  }
 }

 /*adding for stmth */
 switch(stmth)
 {
  case 1:
  case 3:
  case 5:
  case 7:
  case 8:
  case 10:
  case 12:
   days = days + (31 - stdt); break;
  case 4:
  case 6:
  case 9:
  case 11:
   days = days + (30 - stdt); break;
  case 2:
   if((styr % 4) == 0)
   {
    days = days + (29 - stdt);
    break;
   }
   else
   {
    days = days + (28 - stdt);
    break;
   }
 }

 /*adding for edmth */
 days = days + eddt;
 

 if(flag) return -days; else return days;
}

/* End of DMY function  Delete the code that follows below when compiling
for the routine. With the below code it is a stand alone program for DMY */
 

void main()
{
 char stdate[9];
 char eddate[9];
 
 printf("\nEnter start date : ");
 scanf("%s",stdate);
 printf("\nEnter end date : ");
 scanf("%s",eddate);
 
 printf("\n\nDays = %d\n",DMY(stdate,eddate));

 _getch();

}